Pulsed electrolysis

The oxidation potentials of diphenyl selenides ° and diphenyl tellurides have been measured by electrochemical methods, as well as by pulse radiolysis. Pulse electrolysis was used to determine E° values for diphenylsulfide (84), diphenylselenide (85), and diphenyltelluride (23). In each case, equilibrium... 

Surfaces of cadmium with various morphological properties were electro-formed on the Cd electrode from sulfate solutions by varying current densities, temperature, and pulse electrolysis conditions [218]. The surface properties were defined by the values of slopes of quasi-steady state E versus logarithm current density dependencies and exchange current densities in 0.5 M CdS04 + 0.15 M H2SO4 solution. The dependence of the slope values on surface properties was explained in terms of the influence of crystallization overpotential. 

An interesting extension of the cpe technique is pulse electrolysis. The electrode is maintained not at one single potential, but at a series of potentials of controlled duration according to a predetermined program. Tills is done by means of a pulse generator (also commercially available). Pulse techniques have hitherto been used mainly for mechanistic studies 91,92-1 but hold great promise for synthetic applications too 90,2 65 As an example, in the anodic oxidation of aliphatic hydrocarbons in non-aqueous medium at a platinum anode, the electrode activity falls rapidly with time if the potential is kept constant, probably because of the formation of an adsorbed film of intermediates or products. However, regular, short cathodic pulses reactivate the anode and the reaction proceeds without difficulties 30 ... 

Pulse electrolysis. It is a fact ofelectrode kinetics involving gas evolution that pulsing reduces the overpotential for a given current density (Ghorogchian, 1985). With pulses of about 1.5 V, 10 3 s in duration, the saving in electricity costs would be about 15%. 

Sn(II) and Nb(V) species changed their coordinations with the liquid composition. Nb-Sn alloy samples were prepared by the potentiostatic method and analyzed. The results showed that the Nb content in the alloy could be increased by increasing the bath temperature to 160 °C and increasing the NbCh content in the bath. However, increasing the NbCls mole fraction in the bath also increased the viscosity of the bath. Pulse electrolysis was found to be effective in increasing the Nb content in the alloy. The maximum Nb content in the alloy was 60.8 wt% from constant potential electrolysis and 69.1 wt% from pulse electrolysis. XRD diffraction patterns showed that the electrodeposits contained crystalline Sn and NbsSn which is a superconductor material. 

In some anodic reactions, especially in aprotic media, the products obtained form a layer of tarry material on the electrode surface that (by covering it) insulates it electrically from the solution. The removal of this layer and the attainment and maintenance of a clean, reproducible surface are often a major problem in the use of noble metal anodes. Sometimes it is possible to avoid fouling of the electrode by using pulse electrolysis. 

Pulse electrolysis, which is often used to improve the quality of electrodeposits (see below), was found to have a strong effect on the structure of nickel deposits by modifying the interfacial sorption properties [6.62]. Molecular species such as H2 or Ni(OH)2 are easily desorbed during the relaxation time, improving the electrocrystallization process. Conversely, specifically adsorbed species such as Hads or anions inhibit the electrodeposition process of nickel. 

A pulsed electrolysis of COj on Au, Ag and Cu and their alloyed electrodes was performed, laying special emphasis on an improvement of the selectivity of reduction products. The effect of anions (Cl, Br, I ) intentionally added to a KHCO3 blank solution on the selectivity was investigated. The pulsed electrolysis was found to have a remarkable effect in enhancing hydrocarbonization reactions on Ag and Cu, while little on Au. It is concluded that oxide surface formed during an anodic period may play a key role in the selectivity of reduction products of COj. 

Although main reduction product of CO2 on Ag under galvano/potentiostatic electrolysis is CO, CH4 was found to be effectively formed under the pulsed electrolysis at 17=-2.25V and V, =-0.6 -0.4V. The present result shows that the peak potential at which 77 (CH4) and 77 (CO) become a maximum shifts positively. A maximum faradaic efficiency of about 30% for hydrocarbonization reaction on Ag electrode was achieved as shown in Table 1. The yields of hydrocarbons increased while 77 (CO) decreased. 

Similar to this, luminescence appears in the galvanostatic pulse electrolysis of hexamethylphosphotriamide solutions of different salts without the separation of catholyte and anolyte. The authors of Ref. believe that the cation [(CHp NJj P OY, where Y stands for iodine or tosyl (Ts, p—CH CgH SOj") or mesyl (CHjSO ), appears at the anode. The iodine derivative was formed in a reaction between the solvent and the iodine liberated at the anode in potassium iodide solution. The other two compounds were obtained by adding tosyl and mesyl chlorides, respectively to the solution 2 . 

A combination of the pulse electrolysis and the stopped-flow method has been used to study the reactivity of radical cations.A highly reactive transient radical cation can be generated very rapidly and its extremely fast reaction analyzed by the stopped-flow method. The... 

Ethyl 3,5-di-tert-butyl-4-hydroxybenzoate in acetonitrile containing sodium perchlorate and perchloric acid after pulse-electrolysis with a platinum-iridium anode at 1.5v gave ethyl 7-tert-butyl-2-methylbenzoxazole-5-carboxylate in 73% yield (ref. 106). 

Highly regioselective anodic monofluorination of 2-aryl-4-thia-zolidinones 53 can also be promoted by using pulse electrolysis in EtjN-SHF/MeCN as shown in Scheme 41. In this case, benzylic fluorination does not take place and fluorination occurs at the 5-position selectively. The regioselectivity of this process appears also to be controlled kinetically as shown in Scheme 40. The transformation of the sulfones 55 derived from fluorinated products 54 into monofluoro P-lactams 56 is readily performed in excellent yields by thermolysis (Scheme 41). 

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